Beverage dispensing apparatus have heretofore been made in which a flavoring syrup is separately stored and then mixed with water to produce a beverage. It has heretofore been proposed to make a beverage dispensing device utilizing separate water and syrup metering orifices for respectively metering the flow of water and syrup to a dispenser. However, the flavoring syrup concentrate frequently contains or forms gelatinous and or crystaline particles which tend to clog the syrup metering orifice and markedly change the proportions of syrup and water in the mixed beverage. In the prior dispensing apparatus of this type, it was necessary to disassemble the syrup metering orifice and syrup filter in order to clean the same. The disassembly, cleaning and reassembling of the syrup orifices and filters was tedious and time consuming and such prior apparatus were objectionable either as requiring too much operator time in order to maintain proper operation or as being inaccurate in metering if the operator failed to clean the same as often as necessary. In order to overcome the above difficulties encountered in orifice type metering devices, it has also been proposed to use a positive displacement type pump for positively pumping the water and the syrup to the dispenser. While such devices are less susceptible to problems due to gelatinous or crystaline particles in the syrup, they are more complex and hence more expensive to build and difficult to service.
It has also been known to produce semi-frozen or slush type carbonated beverages by passing a carbonated beverage mix to a freezing chamber that refrigerates and agitates the carbonated beverage to form a semi-frozen product. Some prior apparatus operate the freezing chamber at atmospheric pressure. However, the carbon dioxide tends to escape from the beverage at atmospheric pressure, particularly when allowed to stand for a substantial period of time, and the yield or overrun in such apparatus is not as high or as uniform as is desirable. In order to achieve a higher and more uniform yield or overrun, it has also been proposed to operate the freezing chamber at above atmospheric pressure. However, in such pressurized freezing chambers difficulties are encountered in accurately controlling the pressure and liquid level in the freezing chambers.